Bone Remodeling/Repair/Feedback Loops

How often is spongy bone remodeled?

3-4 years

How often is compact bone remodeled?

10 years on average

What is transcytosis?

A process that moves material through a cell from one side to the other

What is bone resorption?

Osteoclasts secrete HCl and lysosomal enzymes which remove a layer of bone and increase the amount of Ca2+ in the blood

How many grams of calcium are in the body?

1200-1400 grams (3lbs)

How many mg/100 mL of calcium are in blood?

9-11

What happens if your calcium level is below 9mg?

Hypocalcemia which results in seizures or spasms

What happens if your calcium level is above 11mg?

Hypercalcemia which results in nausea, vomiting, and kidney stones

What happens if you have high blood Ca2+ levels?

Osteoblasts release osteoprotegrin to the osteoclasts which then decrease bone resorption and decrease the release of Ca2+

What happens if you have low blood Ca2+ levels?

The parathyroid hormone signals the osteoblasts to release a rank ligand. The ligand signals the osteoclast to increase activity to have more Ca2+ in the blood.

What is Wolff’s law?

Bones remodel in response to the demands put on it

What is the evidence for Wolff’s law?

Where stress is greatest, bone is strongest

The least amount of stress on bone is in the medullary cavity

Bones are larger in your dominant hand

List the steps for bone regeneration

Reduction (alignment), immobilization to keeps ends in place, repairing of the bone

What are the steps for bone repair?

Hematoma formation, soft callus formation, bone callus formation, remodeling

What happens during hematoma formation?

Blood clots

What happens during soft callus formation?

Vasculature re-enters the broken area, damaged tissue is removed (debridement), and a bridge of cartilage forms

What happens when bone callus forms?

Osteoblasts ossify in the callus and spongy bone connects

What happens during remodeling?

Osteoblasts and osteoclasts work together to bring the bone back to its original state

What happens when someone has osteoporosis?

Bone volume is decreased because osteoblasts don’t make enough and osteoclasts are too active.

What are some causes of osteoporosis?

Low estrogen levels due to menopause, smoking, or a hypothyroid. Lack of vit D or Ca2+ or a lack of exercise which is Wolff’s Law.

What are some treatments for osteoporosis?

Estrogen therapy, exercise, increased calcium in diet, and increased vitamin D